There are many applications for polishing or very light grinding devices, particularly in the dressing and polishing of internal bores of pipes, etc. In the past, one type of device which has been employed comprised a generally circular hub mounted upon a rotatable arbor in order to drive the hub about its axis. The hub has been provided with lingitudinal slots which extend between the opposite end faces of the hub and open on the periphery thereof. From the periphery, the slots extend, and terminate at, a generally circular bore which also extends between the opposite end faces of the hub. Each slot-bore combination is so configured as to receive and hold a segment in such a manner that the segment is retained in the hub, particularly against centrifugal force generated by the hub's rotation.
In general, the prior art drum segments have comprised a plurality of abrasive flaps of uniform size and shape, joined together along a common edge to form a packet. The packet is fastened to a metal strip comprising a pair of plates or plate sections, one of which is longer than the other. The longer plate or plate section is overlapped with the common edge of the packet so that the two may be joined, for example, by stapling.
The two plate sections of the metal strip are flat, generally parallel to one another, and located in surface-to-surface abutment. They are joined together by a root element which is generally circular in shape. The root element is so configured as to fit within the bore of the hub and the plates fit within the adjoining slot in the hub. The length of the shorter plate has generally been approximately equal to the radial dimension of the slot in the hub to provide full support for the segment in the hub with as little play as possible, thereby minimizing wear, etc.
In general, the circular root element has been employed to firmly fix the segment to the hub and prevent the segment from being pulled radially from the hub by centrifugal force. Although this principle of construction is sound, it has not been totally satisfactory; the high tensile or bending forces exerted on the root element by the segment during polishing operations have caused the root element to flatten out or assume a somewhat tear drop shape. This allows the segments to become misaligned and either so loose within the hub as to be unstable, when the hub is stopped, or to bind within the hub so that they are difficult, at best, to remove.
Further, it has been determined that the formation of the root element causes the junction of the element with each of the plate sections to occur at relatively sharp bends, i.e., angles approaching 90.degree.. It has been determined that these sharp bends lend themselves quite readily to fracture in use, particularly in the plate section to which the packet is joined. Thus, the packet may become misaligned with the hub, at best, and may even pull away from the hub entirely under centrifugal force.
Accordingly, it has become necessary to devise an economical method of overcoming these deformation and fracturing problems in order to allow continued use of these very valuable tools.